Might pay to have a look at the installation instructions www.otenet.gr/hd/HTML/adsl/documents/huaweileafleten.pdf
It would also help to check for the latest firmware on the HG520 models, because sometimes this can be an added bonus on these routers. They do get rather warm while working, and cool-off on standby.
If you want to get into the router, then try 192.168.1.1 in your browser, then put 'admin' in both pass boxes that should appear. But I cannot guarantee that this method will work with your router, but worth a try perhaps?.